1. Field of the Invention
The present invention relates to a technique of providing images excellent in coloring property and homogeneity of color, and particularly to a liquid composition, which is most suitable for use in the formation of images making good use of an ink-jet recording system, and an ink set using the liquid composition, and a method of forming a colored portion on a recording medium and an ink-jet recording apparatus using this ink set.
2. Related Background Art
An ink-jet recording method is a system in which recording is conducted by ejecting an ink to apply the ink to a recording medium such as paper. For example, according to the ink-jet recording method disclosed in JP 61-59911 B, JP 61-59912 B and JP 61-59914 B, in which an electrothermal converter is used as an ejecting-energy supply means to apply thermal energy to an ink so as to generate bubbles, thereby ejecting droplets of the ink, the formation of a high-density multi-orifice in a recording head can be realized with ease, and high-resolution and high-quality images can be recorded at high speed.
However, the conventional inks used in the ink-jet recording method generally comprise water and a colorant as principal components, and include additionally a water-soluble high boiling solvent such as glycol for the purpose of preventing drying of the inks within nozzles, clogging at orifices, and the like. When such an ink has been used to conduct recording on a recording medium, therefore, there have been brought about problems that fixability cannot be sufficiently achieved, and image irregularity occurs, which appears to be attributed to the uneven distribution of a filler and a sizing agent on the surface of recording paper as the recording medium. On the other hand, in recent years, there has been an increasing demand for high image quality for ink-jet recording articles on the same level as that of silver halide photography, and thus, technical requirements for increasing the image density of an ink-jet recorded image, broadening the color reproduction range and further increasing the homogeneity of color of recorded articles have been becoming higher.
Under the circumstances, various proposals have been made with a view to stabilizing an ink-jet recording method and improving the quality of recorded articles obtained by an ink-jet recording method. One of the proposals for the recording medium is a method of coating the surface of the base paper of a recording medium with fillers or sizing agents. For example, a technique of coating a base paper with porous fine particles that adsorb a colorant as a filler to form an ink-receiving layer comprising the porous fine particles has been disclosed and a coated paper for ink-jet printing has been put on the market as a recording material utilizing such techniques.
In order to stabilize an ink-jet recording method and increase the quality of recorded articles obtained by an ink-jet recording method, various proposals have been heretofore made. Some of typical examples thereof have been classified and summarized as described below.
(1) Method of Internally Adding a Volatile Solvent or a Penetrating Solvent to an Ink
JP 55-65269 A discloses the addition of a compound capable of enhancing penetrability, such as a surfactant, into inks as a means for facilitating fixability of the inks. Besides, JP 55-66976 A discloses the use of inks comprising a volatile solvent as a principal component.
(2) Method of Mixing a Liquid Composition that Reacts with an Ink on a Recording Medium
In order to improve image density and water resistance and inhibit bleeding, there have been proposed methods in which a liquid composition, which can make the quality of images better, is applied to a recording medium prior to or after the jetting of an ink for forming recording images. For example, JP 63-60783 A discloses a method in which after a liquid composition containing a basic polymer is applied to a recording medium, an ink containing an anionic dye is applied thereto, thereby conducting recording. JP 63-22681 A discloses a recording method in which a first liquid composition containing a reactive chemical species and a second liquid composition containing a compound reacting with the reactive chemical species are mixed on a recording medium. Further, JP 63-299971 A discloses a method in which a liquid composition containing an organic compound having two or more cationic groups per molecule is applied to a recording medium, and recording is then conducted with inks containing an anionic dye. JP 64-9279 A discloses a method in which after an acidic liquid composition containing succinic acid or the like is applied to a recording medium, an ink containing an anionic dye is applied thereto, thereby conducting recording.
Further, JP 64-63185 A discloses a method in which a liquid composition, which insolubilizes dyes, is applied to a paper prior to application of an ink. Further, JP 8-224955 A discloses a method in which a liquid composition containing cationic substances having different molecular weight distribution regions is used in combination with an ink containing anionic compound. JP 8-72393 A discloses a method in which a liquid composition containing a cationic substance and finely divided cellulose is used in combination with an ink. They each describe that images having high image density, good printing quality and water resistance, and also good color reproducibility and inhibition of bleeding can be obtained. In addition, JP 55-150396 A discloses a method in which after recording with a dye ink on a recording medium is performed, a water resistance imparting agent that forms a lake with the dye is provided, imparting water resistance to recorded images.
(3) Method of Mixing an Ink with a Fine-particle-containing Liquid Composition on a Recording Medium
JP 4-259590 A discloses a method in which after imparting a colorless liquid containing colorless fine particles composed of an inorganic substance onto a recording medium, a non-aqueous recording liquid is applied to the recording medium. JP 6-92010 A discloses a method in which after imparting a solution containing fine particles or a solution containing fine particles and a binder polymer onto a recording medium, an ink containing a pigment, a water-soluble resin, a water-soluble solvent and water is applied thereto. JP 2000-34432 A discloses a recording material that includes a liquid composition containing water-insoluble fine particles and an ink. They each describe that images with good printing quality and coloring property can be obtained.
The inventors of the present invention have made extensive studies on various types of ink-jet recording techniques such as those as described above and as a result they have found that although the above-mentioned techniques exhibit excellent effects for respective technical problems, in some cases other ink-jet recording properties will be traded away. For example, a recording medium obtained by coating a surface of the base paper of a recording medium (hereinafter, referred to as xe2x80x9ccoated paperxe2x80x9d) with fillers or sizing agents has been recognized as a technique capable of forming images with high quality.
Generally, in order to obtain images with high saturation, it is known that the colorant must remain on the surface of a recording medium in a monomolecular state without forming aggregates. The porous fine particles of a coated paper have such a function. However, to provide high image density and high saturation of image, it is essential to form an ink-receiving layer thick enough to shield the base paper with a large amount of porous fine particles relative to the colorant in the ink. This causes a problem that the texture of the base paper will be lost. The inventors supposed that the necessity of an ink-receiving layer so thick as to cause loss of the texture of the base paper would be attributable to inefficient adsorption of the colorant on the porous fine particles.
Taking an example of a coated paper having one ink-receiving layer, explanation will be made as below. FIG. 9 is a schematic cross-sectional view showing a coated paper in the vicinity of the surface thereof. In FIG. 9, reference numeral 901 denotes a base paper and 903 denotes an ink-receiving layer. Generally, the ink-receiving layer 903 has porous fine particles 905 and an adhesive 907 immobilizing them. When an ink is given, the ink penetrates into the interstices between the porous fine particles 905 by capillary action to form an ink-penetrated portion 909. As shown in FIG. 9, the porous fine particles 905 exist in the ink-receiving layer locally in different densities so that the manner of penetration of the ink will differ from place to place. As a result, during the process of penetration of the ink, the colorant cannot uniformly contact the surface of the porous fine particles so that the colorant cannot be efficiently adsorbed on the porous fine particles.
Further, there are portions where the adhesive 907 prevents the penetration of ink, thus generating portions that do not contribute to color development. That is, in conventional coated papers, the colorant cannot be efficiently adsorbed in a monomolecular state in spite of the amount of the porous fine particles, with the result that a large amount of porous fine particles is necessary in order to obtain images with high quality so that the texture of the base paper is deteriorated.
Further studies by the inventors revealed that although the use of the technique (1) described above improves fixability of ink to the recording medium, in some cases a reduction in image density and a reduction in color reproduction range, which is considered to be important for recording on a paper or recording of color images, might occur. Further, the inventors"" studies indicated that the technique (2) described above enabled the colorant in an ink to remain on the surface of a recording medium, thus providing a recorded article with high image density but presumably due to agglomeration of the colorant on the surface of the recording medium it could not in some cases provide sufficient color reproduction range or saturation. Further, although the conventional technique described in (3) above achieved improvement of the surface state of the recording medium by imparting a solution containing fine particles, it could not provide images with high precision and saturation as on a coated paper. Furthermore, in particular in the case of non-aqueous recording solution, there are some limitations on the choice of the colorant and the record imparting method and this problem remains to be solved. As described above, the conventional methods have respective problems to be solved and hence the inventors have come to have a recognition that development of new ink-jet recording technique is necessary for providing ink-jet recorded articles with much higher quality than has been demanded in recent years. The present invention has been accomplished based on this recognition.
Therefore, an object of the present invention is to provide a liquid composition for use in providing high quality ink-jet recorded articles having a much broader color reproduction range and excellent color homogeneity and also a liquid composition that is excellent in reliability in printing, specifically excellent in storage stability for prolonged time in a low temperature or high temperature environment, in preventing the clogging of the ejecting head, and in durability of the head surface against the wiping upon suction recovery. Another object of the present invention is to provide a method of forming a colored portion on a recording medium that can form on a paper an excellent ink-jet recorded article having a much broader color reproduction range, excellent color homogeneity, less occurrence of stripy unevenness in a solid printed portion and that is excellent in reliability in printing, specifically excellent in storage stability for prolonged time in a low temperature or high temperature environment, in preventing the clogging of the ejecting head, and in durability of the head surface against the wiping upon suction recovery.
Further, another object of the present invention is to provide a liquid composition that can form an excellent ink-jet recorded article having a much broader color reproduction range, excellent color homogeneity, less occurrence of stripy unevenness in a solid printed portion and that is excellent in reliability in printing, specifically excellent in storage stability for prolonged time in a low temperature or high temperature environment, in preventing the clogging of the ejecting head, and in durability of the head surface against the wiping upon suction recovery, an ink set containing such a liquid composition in combination with an ink, and a method of forming a colored portion on a recording medium and an ink-jet recording apparatus using such an ink set.
The above-mentioned object will be achieved according to the following aspects of the present invention. Thus, the present invention relates to a liquid composition for use in forming on a recording medium a colored portion by imparting the liquid composition together with an ink containing a colorant to the recording medium, comprising at least a solvent and fine particles reactive with the colorant, wherein the fine particles in the liquid composition have an average particle diameter in a range of 30 to 200 nm, and a 10% cumulative value of scattering intensity of 10 nm or more and 90% cumulative value of scattering intensity of 300 nm or less, when measured by a dynamic light scattering method. Also, the present invention relates to an ink set comprising at least an ink containing a colorant and a liquid composition containing fine particles reactive with the colorant independently, wherein the liquid composition is the liquid composition described above. Also, the present invention relates to a method of forming a colored portion on a recording medium, comprising at least the steps of:
(i) imparting an ink containing a colorant to the recording medium; and
(ii) imparting the above-described liquid composition to the recording medium. Further, the present invention relates to an ink-jet recording apparatus comprising:
an ink-containing unit containing an ink containing a colorant;
a first recording unit provided with an ink-jet head for ejecting the ink;
a liquid-composition-containing unit containing the above-described liquid composition; and
a second recording unit provided with an ink-jet head for ejecting the liquid composition.
The inventors have made extensive studies with a view to solving the problems of the prior art as described above and as a result they have found that use of a dispersion in a solvent of fine particles having the action of adsorbing a colorant in a monomolecular state in order to have the colorant efficiently adsorbed on or combined with the fine particles, together with an ink in a liquid state allows reaction of the colorant and fine particles in a liquid-liquid state, resulting in an improved image density and saturation. The present invention has been accomplished based on this finding. Herein, the term xe2x80x9creactionxe2x80x9d or xe2x80x9creactivexe2x80x9d in the phraseology xe2x80x9cfine particles reactive with the colorantxe2x80x9d or xe2x80x9creaction between the colorant and fine particlesxe2x80x9d means besides covalent bond between the colorant and fine particles, ionic bonds, physical chemical adsorption, absorption, adherence and other interactions therebetween.